1. Field of the Invention
Exemplary embodiments relate to semiconductor memory devices. More particularly, exemplary embodiments relate to semiconductor memory devices having write assist circuits.
2. Description of the Related Art
Semiconductor memory devices are typically classified into volatile memory devices and nonvolatile memory devices. Volatile memory devices lose their stored data when their power supplies are interrupted, while nonvolatile memory devices retain their stored data even when their power supplies are interrupted.
Volatile memory devices include static random access memories (SRAMs) and dynamic random access memories (DRAMs), which are roughly categorized according to data storage schemes. That is, an SRAM stores data by using a latch while a DRAM stores data by using a capacitor. Comparatively, an SRAM is mainly used as a cache memory because its peripheral circuit is simple in configuration and its speed is high despite it having a lower memory capacity than a DRAM, due to its lower integration density.
The miniaturization of semiconductor devices is accelerating with the recent advance in semiconductor manufacturing processes, fueled by increases in the distribution of basic process characteristics of the semiconductor devices. For example, in an SRAM, miniaturization of semiconductor devices has improved due to increases in the distribution of characteristics required for design, such as a write margin and a sense margin. As semiconductor manufacturing processes become finer, the increased distribution leads to difficulties in the development of SRAMs and a reduction in the stability of memory cells. As a result, yield is reduced.